Highway crossing protection system



Aug. 23, 1966 c. w. FAILOR ETAL HIGHWAY CROSSING PROTECTION SYSTEM Filed Feb. 14, 1963 3 Sheets-Sheet 1 Aug. 23, 1966 c. w. FAILOR ETAL HIGHWAY CROSSING PROTECTION SYSTEM 5 Sheets$heet 2 Filed Feb. 14, 1963 y m? m w mm @m w FE L m 5 T w M. w w W Y u wa m 5 H WRQQE QR: m K M n w UHIIU FISW. N Ll I T Row N u k m @gwfib m w wkSuN m m M SON Q8: m NBS: m m W m m m m m m m w @r r fi I N MSW NMQBQHE fiw MRS: WW NR9: NW @N mm E 55w: .1 J. l u H.N.W\ w Q W W W N n as lllllL QSWWQPNU QSE UQQN Aug. 23, 1966 c. w. FAILOR ETAL 3,

HIGHWAY CROSSING PROTECTION SYSTEM 5 Sheets-Sheet 3 Filed Feb. 14, 1963 E mm m g kw? NR \EL u U a m b m. NE SR T Vania Filed Feb. 14, 1963, Ser. No. 258,434 9 Claims. (Cl. 24613t)) Our invention relates to a highway crossing protection system. More particularly, our invention pertains to such a protection system using overlay type track circuits successively in selected zones of a stretch of multiple track railroad in order to protect a plurality of highways intersecting that stretch of track.

Overlay type track circuits are known in the railway signaling art and have been used, particularly in audio frequency form (APO), for highway crossing protection. Frequently, two such track circuits with different frequencies are used in adjoining lengths of track, with a short overlap area spanning the highway crossing itself, to provide a simple system for controlling the warning signal at a single highway crossing in single track territory, signaled or nonsignaled, with two direction running. This typical system is normally applied without installing insulated joints in the rails, other than those already in use by a tratfic control signal system. It has been the custom, where several highway crossings are closely spaced, to assign several distinct frequencies, one to each of such overlay track circuits used in the protection system. This is necessary in order to avoid mutual interference between the track circuits which could result in unsafe operating conditions. Where there are two or more parallel tracks with several highway crossings, the problem of frequency selection increases since, as in any system where alternating currents of higher than commercial frequencies are used, the number of avail-able frequencies is limited in order to provide sufficient separation between those selected. With two or more parallel tracks, the additional problems arise of avoiding interference between the overlay circuits longitudinally along each track and, at the same time, of considering that inductive interference may occur between physically parallel circuits if the same or closely spaced frequencies are assigned to parallel lengths of track.

Accordingly, an object of our invention is an improved highway crossing protection system for closely spaced crossings in multiple track territory.

Another object of our invention is an improved protection system for closely spaced highway crossings using a plurality of overlay type track circuits.

A further object of our invention is an improved arrangement providing protection for several closely spaced highway crossings in multiple track, two-direction running territory of a railroad, using coded, overlay type track circuits having a limited number of different frequencies.

Still another object of our invention is a system for reusing overlay track circuit frequencies in different zones in a highway crossing protection arrangement for multiple crossings in double track territory of a railroad.

It is also an object of our invention to provide an overlay circuit highway crossing protection system for a double track, reverse running railroad with several closely spaced highway crossings, using only a selected number of different frequencies for the overlay track circuits, the use of each frequency being repeated in electrically separated zones of the stretch and with current in each track circuit alternately applied to each of the two parallel tracks.

Still a further object of our invention is a protection system for a series of closely spaced highway crossings along a stretch of-double track rail-road, using a plurality of pairs of overlay type track circuits parallel connected to each of the double tracks, activating current being applied alternately to the circuits of each pair and the assigned frequencies for the plurality of pairs being repeated in different zones of the stretch.

Other objects, features, and advantages of our invention will become apparent from the following description when taken inconnection with the accompanying drawings.

In the description of our invention, we shall refer from time to time to the accompanying drawings in which:

FIG. 1 is a diagrammatic illustration of the basic control circuitry associated with one track at each crossing of a series of closely spaced highway crossings in a stretch of a double track railroad, each track being used for trains running in each direction.

FIGS. 2A and 2B, when placed adjacent horizontally with FIG. 2A to the left, show schematically the track and approach control circuits for the crossing protection system for a double track railroad, with reverse running on each track, where a plurality of highways intersect the railroad within a relatively short stretch.

In each of the drawings, similar reference characters designate similar parts of the apparatus.

We shall now describe our invention, at first generally and then in more specific detail, after which we shall point out the novel features thereof in the appended claims.

Our invention is based on a basic overlap arrangement of overlay track circuits for highway crossing protection. This basic operation or circuitry is utilized in a preselected approach warning distance arrangement to provide a protection system for a series of closely spaced crossings along a stretch of double track railroad over which trains may run in either direction on each track. To reduce the number of frequencies required for the overlay track circuits, coded operation is used. In this manner the same frequencies may be applied to each track of the two, through parallel type connections over dependent front and back contacts, or said in another way, first and second position contacts, of a track coding device or code transmitter. Code detection and/or decoding is then used to determine the nonoccupancy and the completeness of each overlay track circuit. In this manner, any induced interference between the similar, coded parallel overlay circuits in a particular length of the double track interrupts the proper code detection and indicates a fault condition causing a warning signal to be displayed as a fail safe measure.

To further reduce the number of frequencies required for the track circuits, the double track stretch intersected by the series of highway crossings is divided into zones. This division is preferably made at selected crossings, or at the crossing at or near the center of the stretch when only two zones are required. This division is accomplished by inserting a neutral track circuit in each track of the double track, each such circuit being bounded, i.e., insulated or set off from the remainder of the corresponding track rails, by two sets of insulated joints. As specifically shown, the neutral track circuits are island circuits spanning the highway at the selected crossing. This arrangement is preferable for convenience and simplicity of installation and operation, but is notan absolute requirement. The same overlay circuit frequencies can then be used in each zone, that is, the group of frequencies allocated to the entire Warning arrangement may be reused in each zone. The island circuit in each track insulates or blocks interference longitudinally along that particular track between the overlay circuits having the same frequency. In providing for several sections or points of train detection in this preselected distance warning system, a single overlay circuit transmitter may be used to actuate more than one receiver along each track of the parallel tracks. Depending then upon the location of an approaching train, that is, a train moving through the stretch, some of the receivers responsive to a particular transmitter will be active while others will be in a nonactive condition due to the shunt placed on the rails by the train between the transmitter and that particular nonactive receiver. We have chosen to designate the types of circuits used as end fed, center fed, end fed overlap, and center fed overlap track circuits. In this terminology, the term overlap refers to two or more receivers successively connected to the rails in the same direction from a particular transmitter, each responsive to that single transmitter. The rail connections for these overlay circuits are staged, i.e., distributed throughout the stretch and/ or zones, to provide continuous detection of a train moving through the stretch exclusive of any trafiic control signal system in use.

The reception of coded current through the overlay track circuits by a particular receiver is detected by the decoding equipment. Such arrangements, of course, are well known in the railway signaling art. We have chosen to decode the actual code rate, rather than use mere code detection, in order to provide additional protection against induced interference between the track circuits, particularly if coded track circuits are also used for the regular wayside or cab signaling system. The decoding relay associated with each overlay circuit receiver is then the equivalent of the track relay, being energized or deenergized in accordance with the condition of occupancy of the length of track between that receiver and its actuating overlay circuit transmitter. The preselected warning distance is established by repeater relays of these decoding relays. Each repeater relay is responsive to two or more of the decoding or track relays (for the island track circuits) and/or to the operation of another of the re peater relays. The crossing warning signals are actuated to indicate the approach of a train through the operation of the basic circuitry previously mentioned. At each crossing, this circuitry is actually controlled by the repeater relays acting as the equivalent of the usual track relays for such overlap circuits. It is to be noted that, for receding movements of trains, a Warning signal is not actuated. Said in another way, the operation of the warning signal is halted as the train clears the crossing in the receding direction.

We shall now describe the details of our invention both as to apparatus and operation. During this description, reference will be made to the accompanying drawings in which standard or conventional symbols are used to illustrate the various items of apparatus. However, the following specific matters are pointed out in order to assist in the understanding of the circuits shown. Each specific location illustrated is supplied with a relatively low voltage, direct current source of energy. Such use of direct current sources is conventional and any of the several well known types may be used in this type of installation. Accordingly, the sources are not shown as such but connection to the positive and negative terminals thereof at each location are designated by the reference characters B and N, respectively. It is pointed out that, in a system such as illustrated in FIGS. 2A and 2B, it is conventional to connect together the negative terminals of the direct current sources at all locations. Although not shown, such a common connection is herein assumed.

Some of the relays show in conventional fashion are provided with slow release characteristics in order to re- :ain front contacts closed for a selected period after deanergization of the relay winding. These relays are desiglated by downward pointing arrows drawn through the novable portion of each contact of the relays. A specifc example is the directional stick relay ESR shown in the ower left of FIG. 1. In general, contacts actuated by a :pecific relay are shown in vertical alignment with the conventional symbol designating the relay winding. However, to simplify the schematic circuits, some contacts are shown other than thus associated with the winding. Contacts which are so located are associated with the proper relay by repeating the reference character designating the control relay, along with the distinguishing reference for that particular contact. Where relay contacts are normally operating continuously to create or follow a track code, the movable part of such contacts is shown dotted in each of its two positions, i.e., front and back, to conventionally indicate its normal continuous coding operation.

Referring now to FIG. 1, there is illustrated the basic circuitry upon which the system of our invention is based or built. This particular drawing shows the crossing protection circuitry substantially as used in connection with one of the two tracks at highway crossing No. 1 shown in the complete double track system illustrated in FIGS. 2A and 2B. Of course, certain simplifications are possible when only a single crossing is involved. The various modifications which are made in assembling the complete system will be discussed shortly in connection with the description of the arrangement of FIGS. 2A and 2B. In FIG. 1, a length of track 1 is illustrated by a conventional two line symbol, each line of which represents one of the running rails of the track. This length of single track is intersected by highway No. 1 which, of course, in the complete arrangement also intersects the second track of the double track railroad. -A warning of the approach of trains from either direction is provided to the users of highway No, 1 by actuating the crossing warning signals 18 and 28 shown adjacent the highway crossing by conventional symbols. As mentioned, railway trafiic moves in both directions along track 1 as desired in the operation of the railway system. One wayside signal for controlling the movement of westbound, that is, right to left, traflic is shown to the left of the highway crossing. The rails of track 1 are electrically discontinuous at this point because of the insulated joints I which are necessary to the oper ation of the wayside and/ or cab signaling system in general use to control the railway trafiic.

The crossing protection is here provided by two overlay track circuits superposed upon but separate from the regular traffic control signaling system. Each circuit comprises a transmitter and receiver connected to the rails for train detection. Thus the first circuit includes a transmitter No. 1 (west) and receiver No. 1A (west). T he second circuit includes transmitter No. 2 (west) and receiver N0. 2-A (west). These transmitter and receiver units are shown by conventional block diagram since the circuits and apparatus therefor are known in the art. For example, circuit arrangements for such units which may be used in this presentsystem are shown in Letters Patent of the United States No. 3,035,167, issued on May 15, 1962 to P. H. Luft, for a Railway Track Circuit, this patent being owned by the assignee of this present application. Particular reference is made to FIGS. 2 and 3 of this patent for the transmitter and receiver circuits, respectively. Transmitters'and receivers are designated as being for a west zone since identical apparatus will also be used in an east zone of the double track system. The suffixes A modifying each receiver number indicate that additional receivers may be actuated by, that is, responsive to, the same transmitters illustrated.

It is to be noted that each item of the apparatus is energized from the local source of direct current energy, connections to terminals B and N being indicated. It is to be further noted that the receiver responsive to a particular transmitter is connected to the rails on the opposite side of the highway crossing, thus creating an overlap area spanning the width of the highway itself, that is, including the length of rails necessary to span the highway. Such type of circuit connection, that is, the overlap area, is also illustrated in the aforementioned Luft patent (FIGS. 1a, b). Each of the circuits illustrated in FIG. 1 is provided with a different frequency, preferably but not necessarily in the audio frequency range. Another item of apparatus shown by conventional block diagram is the track coupling unit TCU which is necessary to pass the overlay track circuit current of frequency No. 1 around the set of insulated joints J. This item of apparatus is shown conventionally since it is substantially a conventional band pass filter which blocks the direct current or alternating current of lower frequency used in the traflic control track circuits.

As was previously indicated, each overlay track circuit comprises a transmitter and receiver unit connected across the rails of the stretch of track. No insulated joints are needed to separate the operation of this overlay track circuit from the operation of the regular track circuits connected with the signaling system, although a track coupling unit such as TCU may be required if insulated joints are present as part of the regular signaling system. It is to be noted that the output connections of the overlay circuit transmitters are carried over contacts of associated coding devices. For example, the output of transmitter No. '1 is connected to contacts a and b of a code transmitter WC'Dl. Coder WCDI is illustrated as being a relay type coding device, such being well known in the railway signaling art, although other types of coding devices may also be used. Coder WO'I I continuously operates its contacts a and b between a first and a second position, in which front and back contacts, respectively, are closed, as long as the device is energized. Each coder is illustrated as being permanently connected across terminals B and N of the local source. Contacts a and b are operated to close the front and back contacts at a predetermined code rate which may be, as a specific example, 270 times per minute. The actual connection of the output of transmitter No. 1 to the rails of track 1 is over front contacts a and b of coder WCTI so that pulses of current of the frequency of transmitter No. 1 are periodically applied to the rails as the established code rate. Other connections not shown in detail are carried over back contacts a and b of coder NVCTI to the rails of track 2 of the double track railroad illustrated in FIGS. 2A and 2B. This results in pulses of current of the assigned frequency being alternately applied to track I1 and track 2 at the established code rate. The output of transmitter No. 2 is similarly connected over front and back contacts a and b of coder WOTZ to the rails of tracks 1 and 2, respectively. It is to be noted that code transmitters WCTI and WCT2 as well as all other code transmitters used in the complete system herein disclosed, operate at the same code rate.

Current pulses from each transmitter are received through the rails by the associated receiver unit connected in the vicinity of the highway crossing. Reception of these current pulses causes code following operation of the receiver relays WTR1 and ETRl, of the overlay circuits 1 and 2, respectively. This code following operation of the receiver relays is detected in a well known manner by a decoding transformer and decoding unit. The latter unit is tuned, of course, to the selected code rate. A specific example of this operation may be had by considering relay ETRI. When following code, the periodic operation of contact a of relay ETRI between its front and back positions energizes decoding transformer EDT. Specifically, the primary winding is alternately energized in opposite directions by flow of current through the two halves of the winding, current flowing between terminals B and N through the top and bottom halves over front and back contacts a, respectively, of relay ETRl. This alternate reversing of the direction of current flow through the primary winding creates a low frequency alternating current output from the secondary This arrangement incorporates several safety features into the operation of the overlay track circuits. First, there must be code following operation by receiver relay ETRl in order to properly energize decoding transformer EDT to produce an output from the secondary winding of this transformer. Second, this code following operation must be at the proper code rate in order to actuate the unit DU to produce sufficient output to energize relay ECDl. If any induced interference occurs which results in relay ETRl being held energized continuously or being energized at an irregular code rate, relay ECDI will release. Obviously, of course, relay ECDI releases when a train shunts the rails between transmitter No. 2 and receiver No. 2A, that is, between the connections of these two units to the rails and for a limited distance beyond or outside of the connections. Such operation is fully explained in the aforementioned Luft Patent No. 3,035,167. It is obvious from an inspection of the drawing that the operation of relay WTR1, trans-former WD-T and unit DU associated therewith, and decoding relay WCDI is similar to that just described.

Control circuits for crossing relay XR are shown at the bottom of FIG. 1. The circuit arrangement shown is similar to that disclosed in FIG. 1 of Letters Patent of the United States No. 3,004,150, issued October 10, 1961, to M. K. De Vos, for Highway Crossing Protection Systems, which patent is owned by the assignee of this application. It is to be noted that different reference characters are used herein for the track responsive relays, which are here the decoding relays, and for the directional stick relays, which here designate the train direction with which associated. A complete description of the operation of this circuit arrangement can thus be obtained from this reference patent and will be described herein only sufliciently to provide an understanding of the total system of our invention. Briefly, the approach of an eastbound train, that is, from the left, causes the cascaded release of relays WTR1 and WCD1 as this train arrives at the approximate location of the connections to the rails from front contacts a and b of coder WCTl. This action completes the circuit for energizing the eastbound directional stick relay ESR, which, thus energized, picks up to complete its first stick circuit which retains the relay energized after its initial circuit is interrupted by the release of relay XR. This latter relay, having slow release characteristics, holds for a short period before releasing. The closing of back contact b "of relay XR completes the circuit for actuating the crossing signals to warn of the approach of the train.

When the train arrives at the highway crossing, the code following operation of relay ETRI is halted and relay ECDI is deenergized and releases. As the train clears the crossing, the shunt is removed from receiver 1A and relay WTR1 resumes its code following operation, thus causing the reenergization of relay WCDl. With front contact b of relay ESR closed, the circuit is then complete for energizing relay XR which picks up to halt the operation of the crossing signal. The closing of front contact a of relay XR completes a second stick circuit for relay ESR including back contact a of relay ECDI. Since relay ESR is, as shown, provided with slow release characteristics, it holds up for the period of time between the interruption of the first stick circuit and the completion of the second stick circuit. With relay ESR holding its front contacts closed, the circuit remains complete for relay XR and thus holds the crossing signals nonoperating during the period of time that the train is receding from highway crossing 1.

In applying the basic circuits of FIG. 1 to a double track arrangement with a series of highway crossings, each overlay circuit receiver, whether there be one or more than one associated with that particular transmitter, has a code following receiver relay and the associated decoding circuitry. Thus, there is a code detection relay CD associated with each overlay track circuit receiver. The direct or basic control circuits for the warning signals at each highway crossing are of the type shown at the bottom of FIG. 1. However, in most cases, contacts of the code detecting relays CD are replaced by contacts of code detecting repeater relays CDP. This substitution is indicated by the reference character shown in parentheses above the contacts of code detecting relays used in the basic control circuitry at the bottom of FIG. 1. The code detecting repeater relay at a particular crossing, as will become apparent shortly, checks the condition of various code detecting relays CD and track relays TR of the neutral track circuits within a preselected warning distance for that particular crossing. The CDP relay is thus responsive to the occupancy condition of the track throughout the approach warning distance. With the insertion of contacts of repeater relays CDP, control circuit operation is identical with that previously described but covers the entire approach warning distance preselected for that particular crossing. As indicated previously, a control circuit arrangement such as that shown at the bottom of FIG. 1 is provided for each track at each of the series of highway crossings.

Referring now to FIGS. 2A and 2B, we shall describe an installation including one arrangement of our invention as applied to a crossing protection system for a stretch of double track railroad intersected by a series of relatively closely spaced highway crossings. When placed adjacent horizontally, FIGS. 2A and 2B provide a schematic drawing showing the apparatus and circuits for the crossing protection system in a very conventional manner familiar to the art. Each track of the double track railroad is shown by a conventional single line symbol. Trains are operated in each direction on each one of the two tracks. The stretch of double track shown is intersected by nine highways. It is assumed that the railroad is provided with a trafiic control system although only one signal is shown for each track positioned to control conventionally a right hand running train. This trafiic control signal system may use coded or noncoded direct current or alternating current track circuits to which cab signal apparatus may be added. The transmitters and receivers for the overlay track circuits which will be described are shown by conventional blocks designated by the reference characters T and R, respectively. Numerical suffixes are added to distinguish between the apparatus comprising the different overlay track circuits.

Each of the highway crossings, which for convenient reference are numbered across the top of the track diagram from left to right, is provided with a warning signal or signals to indicate to highway traffic the approach of a train. These signals may be of any known type, for example, they may be sets of flashing light signals combined with automatic crossing gates. The approach control circuits for these crossing warning signals are shown below the track diagram but only for track 1, since the arrangement for each track is substantially the same. The system used is based on providing a preselected approach warning distance for each of the crossings, this warning distance varying from crossing to crossing in accordance with the maximum allowed train speed throughout the stretch and other local conditions.

Train detection for this warning system is provided by coded overlay track circuits which are shown in connection with the track diagram in conventional manner using block diagrams. Transmitters are indicated by the reference character T with a sufiix designating the particular frequency channel which is generated by that transmitter. The overlay receivers are indicated by the general reference character R, with a sufiix for the frequency channel which they receive from the corresponding transmitter driving that particular group of receivers. Contacts of the code transmitters CT are also indicated conventionally, the single set of dependent front/back contacts shown for each code transmitter representing the pair of contacts a and b shown in the detailed circuits of FIG. 1. A single conventional contact of a code transmitter, con- 8 tinuously operating between its front and back positions, is thus associated with each of the overlay circuit transmitters. character CT designating each coding contact represents the zone in which the contact is located while the numerical sufiix is related to the transmitter with which it is I associated.

The stretch of double track involved is divided into two zones as shown across the top of the drawing, a west zone and an east zone. This division is accomplished by the neutral track circuits XT and XTA which span the center highway of the series, that is, at crossing No. 5. These circuits are insulated from the remainder of the track rails by insulated joints, shown conventionally and designated by the symbols J1 and J2 on the west and east side of the crossing, respectively. The rails of each track of the double track are thus electrically discontinuous at this center crossing. In other words, the track in one zone is electrically separated from the track in the other zone. It has been found that, with two sets of insulated joints in each track, the same frequency allocations for the overlay track circuits may be used in each zone withi out any interference longitudinally along a particular track. As previously described, coding is then used to detect any induced cross interference between the parallel circuits in each of the two tracks of the double track. Thus, a single overlay transmitter having a particular frequency output may be used to supply parallel overlay circuits extending over substantially the same length of track rail in each of the two tracks.

Each overlay transmitter thus 'actuates two sets of receivers, one set associated with each track. The resulting overlay circuits are then of the nature of parallel circuits actuated alternately from the transmitter at the code rate selected for the code transmitters. In the actual illustration shown, each overlay track circuit, with a single exception, has more than one receiver unit. Where the receivers are all in one direction from the transmitters, the circuit is classified as an end fed circuit. A simple end fed circuit, and the single exception, is shown by overlay circuit 3 in track 2 in the east zone, comprising transmitter T3 and receiver R3 at crossing 8 in track 2. An end fed overlap circuit in which the receivers are connected in one direction successively away from the transmitter is shown by the corresponding third overlay circuit in track 1 of the east zone, which includes transmitter T3 and receivers R3 at crossings 8 and 9 in track 1. Where the receivers extend in both directions from the overlay transmitter, the track circuit is classed as being center fed. A simple center fed track circuit is shown by overlay track circuit 2 in the east zone (either track), which includes transmitter T2 and receivers R2 at crossings '6 and 8. Another type of center fed circuit includes more than one receiver in each direction from the corresponding transmitter and is designated a center fed overlap circuit. One such circuit is illustrated by overlay circuit 2 in the west zone, consisting of transmitter T2 and receivers R2 connected to the rails at crossings 1, 2, 3, and 4 in both tracks. For purposes of the following operational description, it is assumed that in general a receiver is shunted and thus inoperative when a train occupies the track between the rail connections of that overlay receiver and its corresponding overlay transmitter. For simplicity, the relatively short distance outside the receiver and transmitter rail connections in which the shunt is also effective will not be considered. As described previously, when the receiver is shunted, the associated code detecting relay is released. At all other times, the associated code detecting relay CD is energized through the decoding circuits associated with the receiver and is picked up.

In the approach Warning distance crossing signal control circuitry shown below the track diagram, only those relay symbols are included which are used in the individual crossing signal circuits illustrated in the bottom of The prefix letter (W or E) for the reference FIG. 1. In general, such relays are the code detecting repeater relays, each of which repeats the position or condition of more than one of the code detecting relays CD which are directly responsive to the overlay circuit receivers. In the reference characters for the code detecting repeater relays, the numerical suffix is the same as the crossing number with which the relay is associated in the single track control circuitry. The prefix W or E used with the reference characters of the CDP relays indicates the direction from which the relay controls, that is, the direction from which the train is approaching when the relay becomes deenergized. This agrees with the CD relay references used in the basic circuitry of FIG. 1. In connection with crossings 1 and 2, the WCD relay, shown as relays WCD1 and WCD2, are directly involved in the basic control circuitry and thus the symbols are shown but without control circuits which are similar to those shown in FIG. 1. Other code detecting relays CD are represented only by their contacts used in the circuits controlling the repeater relays. Such contacts, properly referenced, are shown in vertical column directly under the overlay circuit receiver by which the corresponding relay is controlled. It is to be noted that the decoding circuits for the CD relays controlling these contacts are as shown in FIG. 1.

Also included in the control circuits for the repeater relays are contacts of track relays, for example, track relay XTR, to which the control circuitry must be responsive. Each of the neutral track circuits shown in the track diagram is provided with a track relay such as relay XTR for neutral track circuit XT spanning crossing 5 in track 1. The neutral track circuits T1 and T2, in track 1 beyond the east zone of the overlay circuits, are provided with track relays TRl and TR2, respectively No relays are shown for the neutral track circuits in track 2 since the control circuitry for the warning signals for this track is not shown. Each of the track relays in the neutral track circuits in track 1 is shown conventionally connected to the track circuit for control purposes in a well known manner. As is well known, each of these track relays is picked up when the corresponding track circuit is not occupied by a train and becomes deenergized and releases when that track circuit is shunted by a train occupying that section of track. Contacts of these track relays which enter into the control circuit are shown directly below the symbol for the relay winding in the usual conventional manner.

We shall now describe the operation of the arrangement including our invention as shown in FIGS. 2A and 2B. Assuming that an eastbound train, that is, one moving from left to right, is approaching on track 1, we shall begin our description with the operation occurring at highway crossing No. 1. As this train passes the location at which transmitter T1 is connected to the rails over front contacts of coder WCTl, the supply of current pulses is shunted in this overlay track circuit so that receiver R1 at crossing 1 is no longer responsive and relay WCD1 releases. Receiver R1 at crossing 2 also becomes nonresponsive at this time, causing the release of relay WCD2. Referring to the circuitry at the bottom of FIG. 1, it is obvious that the release of relay WCD1 at crossing 1 actuates the highway warning signal at this location. Correspondingly, the release of relay WCD2 at crossing 2 actuates the operation of the highway signal at that crossing at the same time. In the circuitry for crossing No. 1 (refer to FIG. 1), relay ESR picks up at this time and completes its stick circuit prepared when relay WCD1 releases.

When the train arrives at crossing 1, relay ECD1 releases as the train occupies the rails between receiver R2 and the connection of the corresponding transmitter T2 further to the east. It is to be seen that the opening of front contact 0 of relay ECD1 interrupts the circuit for repeater relay ECDP1 which thereupon releases. Contacts of this latter relay, of course, are actually used in the control circuitry for the highway crossing signals. As the train clears crossing 1, relay WCD1 is again energized and picks up. With relay ESR already picked up, crossing relay XR is now energized and picks up to halt the operation of the warning signal. Relay ESR will remain energized, with the completion of its second stick circuit, as long as relay ECDPl remains released. This holds the crossing signal nonoperating with respect to track 1, unless another train approaches from the west, while the train is moving away from crossing 1.

When relay ECD1 releases, the opening of its front contact d interrupts the circuit for relay WCDP3 at crossing 3 so that this relay releases to actuate the operation of the warning signal at this crossing. As the train advances further through the stretch, its arrival at crossing 2 causes the release of relay ECD2 when receiver R2 at this location is shunted from its transmitter T2. The opening of front contact 0 of relay ECD2 deenergizes relay ECDP2 which releases to prepare the circuits for halting the operation of the crossing signal and retaining it nonoperating after the train clears the crossing. In addition, the opening of front contact d of relay ECD2 deenergizes relay WCDP4. This latter relay releases to actuate the warning signal at crossing 4. At substantially the same time, due to the opening of front contact 0 of relay WCDP4, relay WCDPS at crossing 5 is deenergized and releases to actuate the operation of the warning signal at this location. Thus it may be noted that the warning signals at crossings 4 and 5 begin operation at substantially the same time during the approach of the eastbound train.

When the train passes the location at which transmitter T2 is connected to the rails of track 1 over front contacts of coder WCT2, overlay circuit receivers R2 at crossings 3 and 4 are shunted from their source of current pulses. Relays WCD3 and WCD4 associated with these receivers, respectively, are deenergized and release. The release of these two relays further interrupts the circuits for repeater relays which are already released, thus assuring the continued operation of the warning signals at crossings 3 and 4 after the train clears the connections of transmitter T2 to the rails and receivers R2 at crossings 1 and 2 are reenergized. The opening of front contact e of relay WCD4 interrupts the circuit for repeater relay WCDP6, this latter relay releasing to initiate the operation of the warning signals at crossing 6. It is believed that the continued operation of the approach control system for the Warning signals at the subsequent crossings and the halting of the operation as the train clears the crossings is obvious from the circuits already traced. Other circuits may be traced as desired by reference to the drawings and the operation already described.

It is to be noted that each crossing has two track responsive relays to control the actual operation of the warning signal, that is, the operation of the basic circuits similar to those shown at the bottom of FIG. 1 which control the warning signals at a particular crossing. In general, these track responsive relays are the code detecting repeater relays CDP, contacts of which replace the contacts of relays CD in the circuitry shown at the bottom of FIG. 1. As previously mentioned, however, at crossings 1 and 2 contacts of relays WCD1 and WCD2 are used directly, since train detection throughout the preselected approach warning distance is by a single overlay track circuit. One additional relay is provided for control purposes over and above the contacts of the track relays TR already described. This is the code detection and track repeater relay CDXTPS, which is specifically located with the apparatus at the center crossing, No. 5, where the island track circuit separating the two zones is used. The energizing circuit for relay CDXTPS includes front contacts 0 of relays WCDS and ECD5 and front contact a of track relay XTR. Thus relay CDXTPS repeats the release of any one of these three relays and is primarily provided to save contacts on the various relays Which it repeats which otherwise would be necessary in the various circuits. It is to be noted that, at crossing 5, the code detecting relays WCDS and ECDS are on the west and east side of the crossing, respectively. In other words, because of the island track circuit XT which separates the entire stretch into two zones, the overlay circuits adjacent crossing 5 do not overlap as in the case of the other crossings.

For purposes of providing some additional operational description it will now be assumed that a westbound train approaches from the right along track 1. In connection with this, it is to be noted that track sections T2 and T1 are part of the regular trafiic control signal system and are assumed to be already existing track circuits which may be used for purposes of the crossing warning system. If the length of these regularly installed track circuits is not satisfactory for the warning system, the train detection provided by these circuits is replaced in the warning system by other overlay track circuits. Upon the approach of the westbound train, the release of track relay TRZ as the train occupies section T2 interrupts, at its front contact a, the circuit for repeater relay ECDP9, causing this latter relay to release. This actuates the operation of the warning signal at crossing 9. Referring to the circuits at the bottom of FIG. 1, it is to be seen that, under existing conditions, directional stick relay WSR is also energized and picks up at this time. The first stick circuit for relay WSR is immediately completed and includes back contact a of relay ECDP9.

As the train advances in the westward direction, it occupies section T1, shunting the rails so that relay. TR1 releases. The opening of front contact a of relay TR1 further interrupts the circuit for relay ECDP9 and the opening of front contact b deenergizes relay ECDP8. The opening of front contact of relay ECDP8 interrupts the circuit for relay ECDP7 which likewise releases. Thus, the warning signals at crossings 8 and 7 both start operation at the time that the train occupies section T1. When the train arrives at crossing 9, it shunts the output of transmitter T3 in the rails of track 1, causing the deactivation of receivers R3 at crossings 9 and 8 so that the corresponding relays ECD9 and ECD8 are deenergized and release. The release of relay ECD9 holds its repeater relay ECDP9 released until the train actually clears crossing 9. When relay ECD8 releases, its front contact e interrupts the circuit for relay WCDP9 which releases at this time. The release of relay ECD8 also interrupts the circuit for relay ECDP6, which releases, and opens at another location the circuit for relay ECDP8. The release of relay ECDP6 actuates the operation of the warning signals at crossing 6 and, further, interrupts the circuit for relay ECDPS which likewise releases to actuate the crossing signals at highway 5. Thus, at the time the westbound train arrives at crossing 9 the signals at crossings 6 and begin operation to warn highway ,users of the approach of the westbound train.

When this train clears crossing 9, overlay receiver R3 connected to the rails at that location is reenergized by pulses of current from transmitter T3 so that code detecting relay ECD9 is reenergized and picks up. The resulting reenergization of relay ECDP9 energizes crossing relay XR at that location to halt the operation of the signals. When relay XR picks up, it completes a second stick circuit for directional relay WSR at that location. This stick circuit will hold relay WSR energized as long as repeater relay WCDP9 is deenergized and released. This latter condition holds until this westbound train has cleared island track circuit XT so that relay XTR is reenergized and picks up to close its front contact b.

When the train arrives at crossing 8, code detecting relay WCDS releases due to the shunting of receiver R2 at this location. This release opens, each at another point, the circuits for relays ECDP7 and ECDP6 to hold these relays released when code detecting relay ECD8 picks up shortly as a result of the train clearing the crossing and removing the shunt from the receiver R3 at this location. The opening of front contact c 'of relay WCDS interrupts the circuit for repeater relay ECDP4 which releases to actuate warning signal operation at crossing 4. Repeater relay WCDP8 at crossing location 8 is also deenergized and releases at this time. This prepares a stick circuit which becomes effective as soon as the train clears the crossing to hold the associated westbound directional stick relay WSR energized to retain the signal nonoperative as the train moves away from the crossing. The operation of the warning signal at crossing 8 is halted as soon as relay ECD8 picks up to reenergize repeater relay ECDP8. It is to be noted that relay WCDPS will remain released until this westbound train has cleared highway crossing 4. This results from the inclusion of front contact e of relay CDXTPS in the circuit for relay WCDPS. Relay CDXTPS, once deenergized, remains in that condition until overlay receiver R3 connected to the rails adjacent the west end of the island track circuit is reenergized from transmitter T3 connected to the rails at crossing 4. By reference to the foregoing description of the operation of the system during the movement of the westbound train to clear crossing 8, when taken in connection with the circuit drawings of FIG. 2A and FIG. 2B, it will be possible, as desired, to trace the remaining operation of the warning system for this train. Therefore, further detailed description is not included in this present specification.

From the foregoing descriptions of the partial movement of an eastbound and a westbound train through the stretch, it is obvious that the approach control circuitry such as is illustrated in FIGS. 2A and 2B can be arranged to select other approach warning distances for each crossing in accordance with the scheduled speed of trains. warning distances selected for each track for one particular direction need not be the same, if the scheduled speeds for the two tracks or other operating conditions differ.

Nor is it necessary that the selected distances for opposite directions on one track be symmetrical. It is to be remembered that the typical circuits shown in FIGS. 2A and 2B are for track 1 only and for convenience and simplicity, the selected distances are .relatively symmetrical about each crossing. If the stretch of track is of such length, or the crossings so numerous as to require an unusually large number of approach warning distances, additional zones may be established so that the overlay circuit frequencies may be reused more than once. It is also to be noted that, although preferable, the neutral track circuits separating the various zones need not be installed as island circuits at a highway crossing.

It is thus to be seen that the system of our invention provides an improved warning arrangement, for a series of relatively closely spaced highway crossings in double track territory, using overlay track circuits superposed upon the regular traffic control signal system. Dividing the stretch of track intersected by the highways into zones reduces the number of overlay frequencies required, since the frequencies selected may be used in each zone. quencies required is obtained by the particular use of coded overlay track circuits, alternately feeding the output of a single transmitter over first and second position contacts of a code transmitter into the parallel circuits in each track of the double track. This avoids any requirement for the assignment of different frequencies to parallel lengths of the double tracks. By these arrangements, i.e., zoning and alternate coding, this system avoids mutual interference between the overlay track circuits in a longitudinal direction along a single track and cross interference between parallel circuits in parallel tracks. The overall arrangement eliminates the need for a large number of insulated track circuits to control the crossing warning signals, thus avoiding undue complication of the control circuits for the trafiic control signal system.

Further reduction of the number of different fre- Also, the additional maintenance required by the necessary insulated joints to establish these additional track circuits is entirely eliminated. At the same time, only a minimum number of different frequencies for the overlay track circuits are required. This system of our invention thus provides the desired results with an efiiciency and economy of apparatus that is highly desirable. In an installation similar to that shown herein, it is estimated that thirty-four regular track circuits and sixty-two insulated joints, with various items of associated apparatus and cabling, may be saved, with an additional yearly savings being realized by the elimination of the maintenance of the insulated joints.

Although we have herein shown and described but a single form of highway crossing protection arrangement embodying the system of our invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what We claim is:

1. In a highway crossing protection arrangement for a stretch of multiple track railroad having a plurality of highway crossings, each such crossing being provided with a warning device for highway trafiic, the combination comprising,

(a) a plurality of sets of parallel overlay track circuits, each set serving from a single transmitter having a frequency different from each other transmitter for detecting the presence of a train in predetermined parallel lengths of said multiple tracks,

(1) said predetermined lengths being so positioned throughout said stretch as to provide continuous detection of a train moving on any of said multiple tracks,

(b) a set of coding contacts for each said overlay circuit set continuously operable in succession between a series of contact points and connected for applying the corresponding transmitter signal successively to each of said multiple tracks to eliminate mutual interference between the parallel lengths of track,

(c) an actuating circuit arrangement for each said Warning device controlled by said overlay track circuit sets for operating the associated warning device only upon the approach of train within a preselected distance of the corresponding crossing from either direction on any of said multiple tracks.

2. In a highway crossing protection arrangement for a stretch of multiple track railroad having a plurality of highway crossings, each such crossing being provided with a warning device for highway trafiic, the combination comprising,

(a) a plurality of sets of parallel overlay track circuits, each set serving with a single transmitter having a frequency difierent from each other transmitter for detecting the presence of a train in predetermined lengths of two parallel tracks,

(1) said predetermined lengths being so positioned throughout said stretch of multiple tracks as to provide continuous detection of a train moving on any track,

(b) a set of coding contacts for each said overlay circuit set continuously operable between a first and a second position,

(1) each set of coding contacts being connected for applying the corresponding transmitter signal alternately to each track of the associated pair of tracks, to eliminate interference between the parallel portions of the associated overlay track circuit,

(c) actuating circuits controlled by said overlay track circuits for operating each warning device only upon the approach of a train toward the corresponding crossing from either direction on any track.

3. In a highway crossing protection system for a stretch of double track railroad including a plurality of highway crossings, said stretch being provided with a signal system for governing the movement of trains in each direction on each track, each crossing supplied with a warning device tor highway traflic, said stretch divided at a selected location by a neutral track circuit in each track into two electrically separated zones, the combination comprising,

(a) a plurality of overlay track circuits for each of said zones, each serving both of the double tracks with a single transmitter having a frequency distinct for that zone only,

(b) a set of coding contacts controlling each of said overlay track circuits for alternately applying the corresponding transmitter output to each of said double tracks for detecting the presence of a train in a predetermined length of each track,

(1) said predetermined lengths being so positioned in each zone together with said neutral track circuits for providing continuous detection independent of said signal system of any train moving on each track,

(c) actuating circuits controlled by said overlay circuits and said neutral circuits for successively actuating said warning devices to warn of the approach of a train moving in either direction.

4. In a highway crossing protection arrangement for a stretch of double track railroad having a plurality of highway crossings, each such crossing being provided with a warning device for highway trafiic, the combination comprising,

(a) a first and second zone of selected length within said stretch,

(b) a neutral track circuit in each track bounded by insulated joints for electrically separating said first and second zones,

(c) a plurality of sets of overlay track circuits, each set serving with a single transmitter for detecting the presence of a train in predetermined lengths of said double track,

(1) each transmitter having a frequency diiferent only from each other transmitter of overlay circuits within the same zone,

(2) said predetermined lengths being so positioned throughout said stretch of double track as to provide together with said neutral track circuits continuous detection of a train moving on either track,

(d) a set of coding contacts for each said overlay track circuit set continuously operable between a first and a second position,

(1) each set of coding contacts being connected for applying the corresponding transmitter signal alternately to each track of the associated predetermined length of said double track to eliminate interference,

(e) an actuating circuit for each Warning device controlled by said overlay track circuits for operating that warning device only upon the approach of a train toward the corresponding crossing from either direction.

5. A highway crossing protection system for a stretch of double track railway intersected by a plurality of highways, said stretch of track being provided with a traffic control system governing the movement of trains in each direction on each track, each highway crossing being provided with a warning signal for highway traffic, said stretch being divided into two zones by an island track circuit in each track set off by two sets of insulated joints at a selected one of said crossings, comprising in combination,

(a) apparatus for forming overlay track circuits, each of a selected one of a number of different frequencies,

(b) a plurality of coding devices having contacts continuously operable between first and second positions,

(c) track connections for connecting one overlay track circuit apparatus of each frequency to said doub-le track in staged succession in each of said zones for detecting the presence of a train in a predetermined length of said double track independent of said traffic control system,

(1) each such connection including contacts of one of said coding devices for alternately connecting the associated overlay circuit apparatus to one and to the other of said tracks as said contacts are operated between first and second positions,

(d) actuating circuits controlled by said overlay track circuit apparatus for operating said warning signals to warn only of the approach of -a train from either direction along said tracks toward said crossings.

6. In a highway crossing protection system for a stretch of double track railroad intersected by a plurality of highways, said stretch of track being provided with a tratfic control system for governing the movement of trains in each direction on each track, each highway crossing being provided with a warning signal for highway trafiic, said stretch of track being divided into a first and a second zone on opposite sides of a selected center crossing electrically separated by island track circuits established at said selected crossing by two pair of insulated joints in each track, the combination comprising,

(a) apparatus for forming a selected number of overlay track circuits, each having one of a plurality of diiferent frequencies,

(b) a plurality of coding devices having contacts operable continuously between first and second positions,

(c) track connections for said first zone for connecting one overlay circuit apparatus of each different frequency to the tracks in staged succession throughout said first zone to detect the presence of a train in predetermined portions of that zone,

(d) other track connections for said second zone for connecting another overlay circuit apparatus of each frequency to the tracks in staged succession throughout said second zone to detect the presence of a train in predetermined portions of that zone,

(1) each track connection including contacts of one of said coding devices to alternately connect the associated overlay circuit apparatus to one and to the other of said double tracks as said contacts are operated between first and second positions,

(e) an actuating circuit for each warning signal controlled by said overlay track circuit apparatus for operating that signal only during a preselected distance of travel prior to the arrival at that crossing of a train approaching from either direction on either track.

7. In a highway crossing protection system for a stretch of double track railroad intersected by a plurality of highways, over which stretch of track trains at times move in each direction on each track, each highway crossing being provided with a warning signal for highway traffic, the combination comprising,

(a) a first and a second track zone on opposite sides of a selected center crossing,

(b) island track circuits established at said selected crossing by two pair of insulated joints in each track for electrically separating said first and said second zones,

(0) apparatus for forming a selected number of overlay -track circuits, each having one of a plurality of different frequencies,

((1) a plurality of coding devices having contacts continuously operating between first and second positions,

(e) track connections for said first zone for connecting one overlay circuit apparatus of each different frequency to the tracks in staged succession throughout said first zone for continuously detecting the presence of a train in that first zone,

(f) other track connections for said second zone for connecting another overlay circuit apparatus of each frequency to the tracks in staged succession throughout said second zone for continuously detecting the presence of a train in that second zone,

(1) each track connection including contacts of one of said coding devices for alternately connecting the associated overlay circuit apparatus to one and to the other of said double tracks as said contacts are operated between first and second positions,

g) an actuating circuit for each warning signal controlled by said overlay track circuit apparatus for operating that signal prior to the arrival of a train approaching that crossing from either direction on either track only when said train occupies preselected approach warning distances established by said overlay track circuit apparatus.

8. In a highway crossing protection arrangement for a stretch of double track railroad having a plurality of highway crossings, each crossing being provided with a warning device for highway traffic, said stretch being provided with a signal system for governing the movement of trains, the combination comprising,

(a) a first and a second zone of selected length within said stretch of double track,

(.b) a neutral track circuit in each track bounded by insulated joints for electrically separating said first and second zones,

(c) a plurality of overlay track circuits, each having a frequency assigned from a plurality of different frequencies less than the number of such overlay circuits,

(1) each overlay circuit being independently operable When superposed on said signal system for detecting the presence of a train in a predetermined length of said double track,

(d) a plurality of coding devices having contacts continuously operable between first and second positions, one device associated with each of said overlay circuits,

(e) the transmitter track connections for each of said overlay track circuits including a contact of the corresponding coding device for connecting that transmitter alternately to each track of said double track at a selected supply location,

(1) said transmitter track connections for said plurality of overlay circuits being selectively distributed throughout said stretch for connecting a single overlay circuit of each of said different frequencies in each of said first and said second zones for providing continuous detection of a train moving on either track,

(f) approach warning distance circuits controlled by said overlay track circuits for recording the passage of a train at predetermined approach locations in said stretch,

(1) each approach location representing a preselected approach Warning distance for at least one of said crossings,

(g) an actuating circuit for each warning device controlled by said approach Warning distance circuits for operating said device to its Warning condition only after an approaching train reaches the corresponding approach location -for that direction of travel, said warning device being held inoperative at other times.

9. In a highway crossing protection system for a stretch of double track railway intersected by a plurality of highways, said stretch of track being provided with a trafiic control system governing the movement of trains in each Qi QGI QIl 011 each track, each highway crossing being provided with a warning signal for highway traffic, the combination comprising,

(a) an island track circuit in each track set off :by two sets of insulated joints at a selected one of said crossings for dividing said stretch into two zones electrically separated,

(b) apparatus for establishing overlay track circuits,

each of a selected one of a number of different frequencies,

(c) a plurality of coding devices having contacts continuously operable between first and second positions,

((1) track connections for connecting one overlay track circuit apparatus of each frequency to said double track in staged succession in each of said zones for detecting the occupancy of a predetermined length of said double track by a train,

(1) each such connection including contacts of one of said coding devices for alternately connecting the associated overlay circuit apparatus to one and to the other of said tracks as said contacts are operated between first and second positions,

(2) said connections being staged throughout said stretch for continuously detecting the occupancy of each zone by a train,

(e) approach warning distance circuit apparatus controlled by said overlay track circuits in accord with detected train occupancy 'for recording the passage of a train at predetermined approach locations in said stretch,

(1) each approach location representing a preselected approach warning distance for at least one of said crossings,

(f) an actuating circuit arrangement for each warning signal controlled by said approach warning distance circuits for operating that signal to warn of an approaching train only after that train reaches the corresponding approach location for its direction of travel, said warning signal being held nonoperating at other times.

References Cited by the Examiner UNITED STATES PATENTS 2,248,397 7/194-1 Thompson 246-130 2,881,309 4/1959 Fodge 246130 3,004,150 10/1961 De Vos 246-130 3,025,393 3/1962 Crain 246-34 X 3,035,167 5/ 196'2 Luft 246-130 3,046,392 7/1962 -Luft 246-130 3,046,454 7/1962 Staples 24634 X 3,069,542 12/1962 Failor 246130 X FOREIGN PATENTS 1,005,553 3/1957 Germany.

ARTHUR L. -LA POINT, Primary Examiner.

S. B. GREEN, Assistant Examiner. 

1. IN A HIGHWAY CROSSING PROTECTION ARRANGEMENT FOR A STRETCH OF MULTIPLE TRACK RAILROAD HAVING A PLURALITY OF HIGHWAY CROSSINGS, EACH SUCH CROSSING BEING PROVIDED WITH A WARNING DEVICE FOR HIGHWAY TRAFFIC, THE COMBINATION COMPRISING, (A) A PLURALITY OF SETS OF PARALLEL OVERLAY TRACK CIRCUITS, EACH SET SERVING FROM A SINGLE TRANSMITTER HAVING A FREQUENCY DIFFERENT FROM EACH OTHER TRANSMITTER FOR DETECTING THE PRESENCE OF A TRAIN IN PREDETERMINED PARALLEL LENGTHS OF SAID MULTIPLE TRACKS, (1) SAID PREDETERMINED LENGTHS BEING SO POSITIONED THROUGHOUT SAID STRETCH AS TO PROVIDE CONTINUOUS DETECTION OF A TRAIN MOVING ON ANY OF SAID MULTIPLE TRACKS, (B) A SET OF CODING CONTACTS FOR EACH SAID OVERLAY CIRCUIT SET CONTINUOUSLY OPERABLE IN SUCCESSION BE TWEEN A SERIES OF CONTACT POINTS AND CONNECTED FOR APPLYING THE CORRESPONDING TRANSMITTER SIGNAL SUCCESSIVELY TO EACH OF SAID MULTIPLE TRACKS TO ELIMINATE MUTUAL INTERFERENCE BETWEEN THE PARALLEL LENGTHS OF TRACK, (C) AN ACTUATING CIRCUIT ARRANGEMENT FOR EACH SAID WARNING DEVICE CONTROLLED BY SAID OVERLAY TRACK CIRCUIT SET FOR OPERATING THE ASSOCIATED WARNING DEVICE ONLY UPON THE APPROACH OF TRAIN WITHIN A PRESELECTED DISTANCE OF THE CORRESPONDING CROSSING FROM EITHER DIRECTION ON ANY OF SAID MULTIPLE TRACKS. 